Arbitrary Bias Point Control for Mach-Zehnder Modulator Using a Linear-Frequency Modulated Signal

A versatile arbitrary bias control technology for Mach-Zehnder modulators (MZMs) based on a linear-frequency modulated (LFM) signal is proposed. An LFM signal is applied to the direct current (DC) port of an MZM together with a DC voltage. The output microwave signal is measured and cross-correlated with the fundamental and frequency-doubled components of the LFM signal. Their ratio serves as the feedback signal to control the bias point. An experiment is carried out. Compared to the conventional single-frequency pilot-based bias control technique, the peak power of the LFM component in the output electrical signal decreases by more than 27 dB, and the error vector magnitude (EVM) of the output microwave signal evaluated by 1000 symbols is reduced from 13.632% to 5.929%.